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The focused ion beam technique - eine interessante Alternative, auch für konventionelle Werkstoffe
(2002)
XTEM and TFXRD investigations of ohmic Ti/Al/Ti/Au/WSiN contacts on AlGaN/GaN HFET layer systems
(2002)
The microstructural features of the high-temperature-stable ohmic contact system Ti/Al/Ti/Au/WSiN on AlGaN/GaN were investigated using analytical transmission electron microscopy and thin film x-ray diffraction.
For two typical rapid thermal annealing steps at 750 ◦C (non-ohmic behaviour) and 850 ◦C (ohmic behaviour) the intermetallic phases at the metal–semiconductor interface are presented. Increased annealing leads to the transformation of an Al2Au-AlAuTi phase mixture to a mixture of Al2Au-Al3Au8 phases and the formation of Ti-Al-nitride layers at the interfaces. In light of these results the electrical contact properties are discussed.
Recent progress in the development of A1GaN/GaN heterostructure field effect transistors (HFETs) Shows the great potential towards high temperature / high power electronics. Nevertheless investigations on reliability properties of GaN-based devices are still at the beginning. The frequently used Ti/A1 based ohmic and Pt based Schottky contacts suffer from strong Degradation after aging at elevated temperatures. Therefore new contact systems have to be employed. Concerning the source and drain metallization we used an amorphous WSiN barrier layer as applied for GaAs on top of the Ti/Al-based ohmic contact. This technique significantly reduces the in-diffusion of the Au-containing overlayer, furthermore the barrier layer guaranties smooth contact morphology after RTA and aging, respectively. For the Schottky metallization the Ir/Au system was used. Reliability studies performed on HFET devices containing refractory Ti/A1/Ti/Au/WSiN ohmic and Ir/Au Schottky contacts demonstrate stable conditions during 120h aging at 500°C.
In the past few years, it has been discussed with increasing frequency, whether cube slip does occur in gamma' hardened nickel-base superalloys. Occurrence of cube slip has consequences for the modeling of orientation dependence of the CRSS. Until now, there are only few experimental investigations.
In principle, cube slip should be possible in primitive cubic lattices (e.g. L12 ordered gamma' phase) but not in face centered cubic ones (e.g. Ni solid solution). The most favourable specimen orientations are near [111], where the Schmid factors for this type of glide exceed those for octahedral systems.
There are two basic methods to detect cube slip: macroscopic slip trace analysis and Transmission electron microscopy (TEM) investigation of the dislocation structure. Few observations of cube slip by macroscopic slip traces are reported in the literature. But it is still uncertain under which test conditions cube slip occurs and what the dislocation mechanisms are. Cube slip was observed during tensile or compression tests of several first generation superalloys, but it seems not to occur during shear creep deformation (e.g. CMSX-4 at 980°C), and it is also lacking under conventional tensile or compression loading, if the gmma' particles are small. No observations were ever reported of dislocations gliding on {001} planes in matrix channels.
The formation of AlN films prepared by N+2 ion implantation into aluminium was investigated using X-ray and Auger photoelectron spectroscopy ( XPS, AES) as well as cross-sectional transmission electron microscopy (XTEM). After 100-keV N+2 implantation of low doses (1×1017 cm−2), the formation of hexagonal AlN nanocrystals (crystal size <5 nm, Ncrystal=1017 cm−3) was observed. Their orientation is strongly correlated with the aluminium matrix. With the dose increasing to 3×1017 cm−2, crystal growth follows, finally forming a homogeneous AlN-layer. Furthermore, the diffraction patterns show an increasing amount of misorientation with increasing dose. From the crystal size distribution, we conclude that continuous nucleation takes place. Samples implanted with an energy of 3 keV exhibit analogous behaviour. Nitride growth was further investigated using microstructured AlN formed by 3-keV implantation through movable TEM-masks (structure size: 15–150 mm).
In the case of high N+2 doses (D&5×1017 cm−2), AlN is detected by AES in the shielded area at a distance of up to 10 mm from the exposed region. The Diffusion coefficient was calculated to be 10−10 cm2 s−1. The formation of AlN proceeds in two steps.
After a continuous nucleation, diffusion-assisted Crystal growth takes place until a homogeneous AlN layer results.
Platinum does not form any adherent oxides and can be easily wetted by tin-based solders. Platinum is also an available metallization in semiconductor laboratories. Therefore we investigated the diffusion of platinum thin-film metallizations into eutectic tin–lead solder by using a high-resolution secondary ion mass spectroscopy (SIMS) profiling from the back side. It is shown that an intermetallic phase (PtSn4) is formed during soldering, which controls the consumption of platinum during soldering and in operation. The consumption of platinum follows the well-known parabolic diffusion law. The activation energy of this process is 0.63 eV. Even at extended heating cycles of 2 min at 250°C, 190 nm from the original 300 nm of the platinum film remain undissolved. This high stability makes platinum a very attractive thin-film metallization for flip-chip (FC) bonding of new microsystems.
An extended model of the tension-compression asymmetry of single crystal nickel-base superalloys
(1996)
Interrupted LCF-tests at 850 deg C for Inconel 738LC have been carried out and the specimens have been intensively examined by REM to quantify the evolution of fatigue damage. Surface crack nucleation at oxidatized grain boundaries and coalescence of neighboring flaws occurred during the whole experiment. An anomalous fast single crack growth is observed just after nucleation, followed by a relative stagnation of the propagation in absence of coalescence. A statistical model is proposed that describes these pheonmena. It leads to an integro-differential equation for the crack density f(c,n) after n cycles, similar to the Bolzmann equation which describes the collision of molecules in a dilute gas.
Transmission electron microscopy study of rapid thermally annealed Pd/Ge contacts on In0.53Ga0.47As
(1996)
Phase formation in rapid thermally annealed Pd/Ge contacts on In0.53Ga0.47As has been investigated by means of cross-sectional transmission electron microscopy, convergent-beam electron diffraction, and energy-dispersive x-ray analysis. Solid-phase regrowth is observed to occur similarly as in Pd/Ge contacts on GaAs or InP. The reaction starts at low temperatures with the formation of an amorphous Pd–In–Ga–As layer, which crystallizes at elevated temperatures yielding hexagonal Pd4In0.53Ga0.47As being first described in this work. At temperatures .250 °C, this phase decomposes due to epitaxial solid-phase regrowth of In0.53Ga0.47As and formation of Pd–Ge phases. The stable composition is reached at temperatures .350 °C with excess Ge diffused through top Pd–Ge to the contact interface and growing epitaxially on the semiconductor.
TEM study on the effect of machining on the microstructure of a soft magnetic Ni76Fe17Cu5CrMo2 alloy
(1991)
The role of grain size and ferrite substructure in respect to mechanical properties of an HSLA steel
(1986)
Several heat treatments were applied to an HSLA steel on type StE460 (German standard) to produce four ferrite substructures of different strength and at least two different grain sizes respectively. Whereas the ferrite substructure has a strong influence on yield strength the effect of grain size was negligible though probably to some extent masked by different pearlite volume fractions. The different strength levels could be explained by regarding the arrangement of dislocations and vanadium carbonitride particles and their mutual interaction. Increasing both grain size and pearlite volume fraction leads to a remarkable shift of transition temperature T sub 27J which was further enhanced by increasing ferrite strength. 16 ref.--AA
Optical and electron metallography have been used to investigate the development of different microstructures in Armco Fe after rolling reductions between 0 and 90%. Simultaneously, the orientation distribution functions have been calculated from pole figures obtained by X-ray diffraction. Different stages of texture development could be assigned to typical microstructures. Strain inhomogeneities, such as microbands and shear bands, caused some broadening of the texture and a slight deviation of one skeleton line from the predicted fibre texture component. The decomposition of orientations near {111} < 121 > , and the strengthening of {211} < 011 > after high rolling reductions, was not due to mechanical twinning but could rather be explained by assuming {211} < 111 > slip. 30 ref.--AA